Author here, and yes that is what I claim. This is actually crypto 101 stuff!
1.) Pre computing SHA256 of a small set of numbers (1111111111 - 9999999999) takes only a couple minutes on your average laptop. That is how people find the preimage (password) of leaked password hashes! More sophisticated techniques use rainbow tables etc.
2.) The preimages of Bitcoins, github commits and file hashes have much more entropy to be able to brute force them. Hence, I will not be able to (with todays computing power) find a pre-image of Bitcoin's SHA256 etc. and sadly not become a millionaire overnight :(
3.) Not related to this but hashing functions do get 'weaker' over time as computing power increases. We don't use MD5 anymore for a reason. SHA1 has attacks now (https://shattered.io/). This is why git to move to SHA256 (https://lwn.net/Articles/811068/). n number of years from now, there will be collision attacks on SHA256 as well, at which point we'll have to move to a better, stronger hash!